Integrated circuit memory may be characterized as being either volatile or non-volatile. Volatile memory must be reprogrammed/rewritten, typically multiple times per second, due to charge dissipation. Non-volatile memory, on the other hand, can maintain any of its programmed states without necessarily requiring periodic refresh. Example volatile memory includes Dynamic Random Access Memory (DRAM). Example non-volatile memory includes Static Random Access Memory (SRAM), Flash Memory, and Phase Change Memory (PCM).
There is a continuing goal in the fabrication of integrated circuitry to make individual devices smaller to increase the density of the circuitry, and thereby either reduce the size of the circuitry or enable more circuitry to be packed into a smaller space. Yet, the smaller and denser circuitry must be reliable in operation. Phase change memory is of increasing interest due to its apparent ability to be scaled smaller and maintain reliability.
The primary components of phase change memory are a pair of electrodes having a phase change material sandwiched there-between. The phase change material is capable of being selectively modified in a manner that changes its electrical resistance between at least high and low resistant states which can be “read” and therefore used as solid-state memory. In phase change memory, electric currents of different magnitudes are selectively passed to the phase change material which changes the resistance of the material very rapidly.
Phase change materials are often formed of a combination or alloy of different metals. One metal of interest is antimony. Such might be combined, for example, with one or both of germanium and tellurium to form a GeSb, SbTe, or GeSbTe alloy. Chemical vapor deposition is one method by which such phase change materials may be deposited over a substrate. For example, different deposition precursors comprising one each of germanium, antimony and tellurium may be provided in desired quantities over a substrate under suitable conditions such that a GeSbTe alloy is deposited having desired quantities of the respective germanium, antimony and tellurium. Example antimony precursors include tris dimethylamino antimony and organometallics such as tris isopropyl antimony. Such precursors may, however, require substrate temperatures in excess of 400° C. to achieve adequate deposition when used in chemical vapor or atomic layer deposition also using NH3. Such temperatures may be incompatible with features on the substrates, or with other precursors, for example tellurium precursors. Use of temperatures lower than 400° C. may result in no deposition, less than desired deposition, or an unacceptably slow rate of deposition.
Phase change materials may also be used in fabrication of rewritable media, for example rewritable CDs and DVDs.
While embodiments of the invention were motivated in addressing the above-identified issues, the invention is in no way so limited.